The present invention relates generally to telecommunication systems and methods, and more particularly, to a system and method for transporting synchronous optical network data more rapidly using an N terminal high speed transport system coupled between 1:N low speed transport systems.
A synchronous optical network (SONET) is one type of telecommunications network that uses a SONET protocol to define the format of data transmitted across a SONET transport system. SONET systems operate at varying optical rates (i.e., the number of 51 MHz signal equivalents the system transmits on an optical fiber). For example, an OC48 channel transports forty-eight 51 MHz signals, or approximately 2.5 GHz, from transmitter to receiver on a single fiber.
Many telecommunication system users have installed 1:N SONET transport systems for point to point transfer of telecommunications data. A conventional 1:N SONET transport system, as shown in FIG. 1, has one protection channel and N working channels (for example, OC 48 channels) connected between two terminals operable to send and receive data over the N channels. The terminals will typically have the same number of input and output channels at each end of the system. If any of the N working channels in the 1:N SONET transport system fails (due to, for example, failure of either a transmitter or receiver), the terminal will transfer the data flowing over the failed channel to the protection channel. This protects any one failed working channel, but cannot protect data on more than one failed working channel at a time. Therefore, if two (or more) working channels fail at the same time, some data will be lost.
In order to accomplish the protection of data if a working channel fails, a negotiation must occur between the two terminals so that the transmitting terminal switches to the protection line and the receiving terminal receives the data on the protection line. A switching protocol for accomplishing this switching typically uses two bytes in a SONET transport system, the K1 and K2 bytes. Both terminals contain the switching protocol to accomplish the protection when a channel fails. The switching protocol is typically transmitted over the protection channel and is defined by an industry standard. As data traffic increases, a user of a 1:N SONET transport system has several options to increase the data transport capacity. First, a user can add working channels to the SONET system, however, there is a limit to the number of working channels that can run between two terminals in a SONET system. The theoretical limit is fourteen working channels as defined by the protocol, however, the practical limit is typically less than fourteen working channels due to current equipment and reliability constraints. The more working channels a SONET system incorporates, the more likely two or more working lines will fail at the same time, resulting in the loss of data (because only one protection line exists). Second, a user can add terminals and the fibers constituting channels between the terminals. However, this becomes prohibitively expensive due to the cost of purchasing and laying the optical fiber cabling between terminals (and the expense of additional terminals).
In order to avoid the cost of additional optical fibers, standard 1:M High Speed SONET transport systems have been conceived that connect more rapid 1:M terminals (having one protection channel and M working channels) between sets of the lower speed 1:N terminals, as shown in FIG. 2. The conventional 1:N SONET terminals will connect to a 1:M terminal having higher rate channels coupled to another 1:M terminal. The 1:N terminal sends the data to a 1:M terminal that packages the data, transmits it over the higher rate channel to the receiving 1:M terminal that forwards the data to the appropriate 1:N receiving terminal. Each of the 1:M terminals, similarly to the 1:N terminals, also has a single protection line to protect the information being transmitted between the 1:M terminals. In a 1:M high speed SONET system, the protection is controlled by the high rate system protocol.
Conventional 1:M high speed systems have two major problems: compatibility between the 1:M and 1:N protocols; and building protocols for both the 1:M and 1:N terminals. In a standard 1:M high speed SONET transport system, the 1:N terminals must use exactly the same protocol as the 1:M terminal in order to communicate. This requirement will often not be met when the 1:N terminals are manufactured by a different vendor than the 1:M terminals. To complicate matters further, the standard SONET protocol is such that even when two vendors comply with the standard SONET protocol, the variation allowed between two compliant protocols can result in communication failure between the two protocols.
Furthermore, the switching protocols (and other protocols) must be built and implemented into both the lower rate 1:N system and the higher rate 1:M SONET transport systems. This problem will be exacerbated if a vender of one of the terminals builds a switching protocol that does not conform with the SONET standards.
The present invention provides a system and method for transporting SONET data that substantially eliminates or reduces disadvantages and problems associated with previously developed SONET transport systems and methods.
More specifically, the present invention provides a system for increasing the transport capacity of a SONET transport system. The SONET transport system includes multiple low speed SONET transport systems wherein each low speed SONET transport system can have a pair of low speed terminals connected by N working channels and one protection channel. A clear channel high speed SONET transport system is connected between each low speed SONET transport system. The clear channel high speed SONET transport system has N+1 working channels that each terminate at a high speed terminal. The low speed system protection channels are multiplexed into one channel of the clear channel high speed system, while each working channel of each individual low speed system is multiplexed into different high speed channels.
The present invention provides an important technical advantage by increasing the speed of transport of data over a SONET system without an inordinate increase in the number of optical fibers required to accomplish the transport.
The present invention provides another technical advantage by providing a system that interfaces a high speed transport system between low speed transport system without requiring special protocols created to interface between the high speed and low speed system. By operating a high speed clear channel system between the low speed system, the high speed system is protocol independent.